Abstract:Hot dry rock， a strategic clean energy resource， belongs to the category of solid minerals， and its occurrence conditions are controlled by the geological environment. With the execution of the hot dry rock resource survey project in Henan Province， and the comprehensive study of hot dry rock reservoir-forming characteristics and drilling results at home and abroad， it is inferred that the heat source of hot dry rock is mainly composed of two modes： the heat transfer of intrusive rock mass and the heat transfer of mantle （convective heat transfer of deep buried faults）. The reservoir-forming environment must have three basic conditions： huge and stable high thermal conductivity rock mass， thick and stable low thermal conductivity overburden and heat source. In view of the existing problems in the prospecting theory and drilling for hot dry rock resources， the preliminary prospecting direction and suggestions are put forward.

Abstract:With decline in traditional energy reserves， the development of new geothermal resources such as hot dry rock is particularly important. The requirements of hot dry rock drilling are very demanding for traditional drilling fluid systems due to ultra-high temperature downhole environment. Filtration loss of traditional drilling fluids increases greatly at high temperature， and common additives often cannot perform well. Although common drilling fluids based on “three sulfonate materials” have satisfactory temperature resistance， they contain a large amount of toxic substance， leading to serious pollution； therefore， it is necessary to develop a new environment-friendly drilling fluid system with high temperature resistance. Research on hot dry rock in foreign countries is more than 30 years earlier than that in China， and very important experience and technology has been obtained on high temperature resistant drilling fluids. Though domestic research on hot dry rock just started， a very important research project “Qinghai Gonghe Basin Qiapuqia Hot Dry Rock Project” has already been initiated. This article introduces the current situation of hot dry rock drilling and the performance requirements for drilling fluids， explains their components and design approaches in light of the research progress of domestic and foreign scholars on high temperature resistant drilling fluids and environmentally friendly drilling fluids， and discuss the development trend of hot dry rock high temperature resistant drilling fluids in reference to the characteristics of hot dry rocks so as to provide support for the research of hot dry rock drilling fluid technology.

Abstract:Study of the percolation and heat transfer in fractured rock mass of geothermal reservoirs is of great significance to the exploitation of geothermal resources in hot dry rocks. In this paper， based on a hot rock dry geothermal project， the numerical simulation software of COMSOL Multiphysics is used to study the mechanism of seepage and heat transfer in single fractured rock mass of geothermal reservoirs， with analysis made of the influence of fluid injection velocity and temperature on the temperature field of rock mass and on the geothermal project of hot dry rocks. It is found that the influence of fluid parameters on the rock mass temperature field is mainly reflected in two aspects： influence on the disturbed region and amplitude of the rock mass temperature field， and influence on the time needed for the rock mass temperature field to reach the steady state. Increase of the fluid injection rate will reduce the system service life and the total outlet normal heat value during the service life. When considering the total outlet normal heat flux， there exists an optimal fluid injection rate， which is 0.011m/s in this study. Increase of fluid injection temperatures will increase the service life of the system and the total normal heat flux and total heat at the system outlet. This study provides a theoretical basis for the development and utilization of hot dry rock self-heating resources and a reference basis for the design of engineering operation parameters.

Abstract:In Gonghe Basin， hot dry rock resources are enriched in granite strata with high hardness and strong abrasiveness， and well developed cracks over some well sections， which leads to difficult core drilling. According to the characteristics of hot dry rock formation and coring demand， the KT178 coring tool was developed， and the impregnated diamond coring bit was designed. The drilling tool was a swivel type double tube core barrel， which can be used with the down-hole motor. The strength check of key components， such as outer barrel， core catcher， was emphasized in the design. The drilling tools have been improved and established through two rounds of experiments and optimization at Well GH-01 and GH-02 with fairly intact core samples obtained， meeting the requirements for coring in hot dry rock exploration. The drilling tools can be extended to similar projects with intermittent coring requirements， such as exploration of shale gas and water resources.

Abstract:In order to solve the problem of temperature measurement at high temperature above 200℃ and provide technical support for high-temperature geothermal and hot dry rock exploration， a storage high temperature and high pressure borehole thermometer was developed by using platinum resistance temperature measurement technology and vacuum insulation technology. The instrument is designed for working environment temperature of 300℃ and water pressure resistance of 100MPa. It can be used for borehole temperature measurement at high temperature and high pressure. The instrument has been used in Huire-1 well and GH-01 well，which can meet the borehole temperature measurement requirements.

Abstract:China is rich in geothermal energy， so it is necessary to develop geothermal energy to alleviate China’s increasing dependence on foreign energy； in addition， the prospect of geothermal energy development and utilization is broad. The fracturing monitoring technology with the inclinometer can monitor the development of fracture morphology， particularly the fracture extension direction， and has been widely used in oil and gas development. It plays an important role in guiding the well pattern layout， fracturing process and construction scale. The X1 well in Qinghai Gonghe Basin is difficult to monitor because of its tight and hard lithology， many construction uncertainties and small flow rate； meanwhile， X1 is the first one of geothermal wells to be fractured in China. It is the first time worldwide that inclinometer fracturing monitoring technology is used to monitor the process of HDR geothermal well fracturing treatment. The successful implementation of X1 well fracturing monitoring has explored and enriched the geothermal well fracturing monitoring methods， broadened the application scope of inclinometer monitoring. The important fracture parameters of X1 were obtained by monitoring， which provides basic data for well pattern layout in this area and an important reference example for monitoring and operation with the inclinometer.

Abstract:This paper introduces the application of composite drilling technology of rotary （top drive） drilling and PDM drilling in hot dry rock Well-GR1 in Gonghe Basin， Qinghai so as to improve hot dry rock drilling efficiency and reduce downhole incidents. According to the working characteristics of the PDM drill under high downhole temperature， optimization was conducted of the high temperature resistance rubber， as well as the clearance between the stator and rotor of the PDM drill. It was tested for drilling of the high temperature hot dry rock well （hole depth of 3705m， hole bottom temperature 236℃） for the first time and was successful. It can provide experience for hot dry rock drilling and deep geothermal resource exploration.

Abstract:Different formations can be encountered in drilling engineering. According to the physical and mechanical properties they are classified as isotropic and anisotropic ones. And in most cases they are anisotropic due to the influence of complicated geological conditions. One of their features is different hardness in different directions of loading， leading to borehole deviation， hence compromising drilling rate and quality. Russian researchers have done a lot of research on drill bits and downhole devices used for drilling in the anisotropic formations and good results have been obtained which can provide reference for us in deep drilling.

Abstract:Washover fishing is a kind of technology to deal with sticking and burial for the purpose of protecting the stuck drill pipe. Optimizing the process parameters of washover operation can improve the success rate of treatment of sticking and burial and reduce economic loss. With analysis and research of the drilling tool combination， drilling process parameters and process method of washover， some notes are put forward for the selection of the drilling tool size， the control requirements of RPM， WOB and ROP in the washover process， the selection and mixing ratio of drilling fluid， and the requirements on cleaning operation during drilling. Field use has proven that the technical measures have good effect on improving the success rate of washover fishing.

Abstract:At present， both at home and abroad are facing serious casing damage problems， so it is necessary to study the influencing factors of casing strength. By establishing a three-dimensional finite element model of casing and cement sheath， and using Ansys finite element analysis software to study the influence of cement sheath parameters， casing eccentricity and ovality on casing strength. The simulation results show that only when the elastic modulus of the cement sheath exceeds a certain value， increasing the thickness and elastic modulus of the cement sheath can improve the strength of the casing， otherwise the equivalent stress of the inner wall of the casing will be increased， and the effect of the cement ring on the strength of the casing is a function of the diameter-thickness ratio of the casing. In addition， the strength of the casing decreases significantly with the increase of the eccentricity and ellipticity of the casing， which can easily cause yield failure of the casing.

Abstract:The main geothermal reservoir is of a thermal karst type in the Niutuo geothermal field in Xiongan New District. In the past， the development was concentrated mainly at the depth less than 1800m， where the length of karst reservoir is 300 to 500m with short open hole section， hence simple drilling. In order to strengthen the exploration of deep geothermal resources and satisfy the needs of the planning and construction of Xiongan New District， investigation of deep geothermal resources was carried out with Wumishan Formation and Gaoyuzhuang Formation as the main targets. The main difficulties included the long open-hole section in the Karst Reservoir， broken formation， circulation loss over long well sections， poor stability of the upper strata. With analysis of drilling problems and difficulties encountered in drilling of the deep thermal exploration wells， the optimization suggestions are put forward for design of the well structure， and the key techniques for drilling in the karst thermal reservoir are summarized so as to effectively improve the safety and stability.

Abstract:As one of the direct and effective means of increasing ROP and efficiency， the vibration impactor is widely recognized and valued in the oil-gas drilling area. This article describes in detail the latest research progress on several kinds of vibration impactors such as the axial impactor， the torsional impactor and the compound impactor， and illustrates that the vibration impactor can effectively enhance the energy of breaking rock， improve the bit condition of breaking rock， and reduce the resistance of breaking rock through reasonable use and conversion of mud hydraulic energy. Field application has shown that the vibration impactor can improve the rate of penetration， and shorten the drilling period.

Abstract:CSD1800ZD automatic core drill is equipped with the automatic detection and control systems for drilling parameters and the automatic rod handling system， which realizes the automation and digitization of drilling process and improves drilling efficiency. In late 2019，the drill was used in Shanwang-Shangmatai mining area in Pingdu city， Shandong province， demonstrating many advantages in drilling performance， easy operation， and automation as an automated core drill. Analysis and summarization is conducted on the application data and field feedback about the drill.

Abstract:The mud pump plays an important role in drilling as the main matching drilling equipment. At present， most of high-power electric driving mud pumps are driven by AC asynchronous motors with the combination of the air bladder clutch， bearing chock and pulley for transmission to achieve speed reduction. With the need of exploration and development of onshore clean energy such as geothermal （hot dry rock）， shale gas， and deep resources， higher requirements are also put forward for high-power electric mud pumps. Through analysis of the requirements of the Xiongan new area geothermal drilling project， the variable frequency permanent magnet motor is adopted to drive directly the pinion shaft of F-1300 mud pump. It has the advantages of simple drive structure， stepless speed regulation， energy saving and high control accuracy， and caters to the development of modern geothermal drilling technology， upgrades the overall level and capacity of drilling rig， and improves drilling efficiency and quality.

Abstract:Nowadays， engineering construction tends to offshore and deep-water areas. As a result， large diameter rock-socketed inclined （RSI） pile has been widely applied in structures foundation in port and dock areas due to its better ability to withstand horizontal loads. However， because of limited construction sites and designed piles parameters etc.， the RSI piles construction is usually carried out by percussion drilling， with its rate of penetration （ROP，0.1~0.3m/h） much lower than that of cast-in-place piles by other construction methods. Based on this， a force model of punch hammer was established in this paper， to study its forced state of dropping process when it is applied to drill a large diameter RSI pile. The influence laws of hammer weight， stroke， pile inclination， and friction coefficient between the punch and steel guard were studied by single-factor and two-factor analyses respectively. According to the analyses， it is found that the hammer weight and stroke are the key factors affecting the ROP of RSI piles when the pile inclination is constant， and the influence of friction coefficient can be ignored to a certain degree.

Abstract:The pile foundation is the most commonly used foundation for buildings in the karst area. The pile foundation construction quality problem is common due to the complexity， particularity， and irregularity of the geological conditions. The main quality problems with the pile foundation in the karst area are pile defects， local pile shaft inclination， thick settlements， and unqualified pile foundation supporting layer. The common test methods for pile foundation include the high and low strain method， ultrasonic method， and coring method. With conventional treatment， high pressure grouting is used to reinforce the pile supporting layer. In regard to a project completed in the karst area in the Longgang District of Shenzhen， an in-depth exploration of pile testing and defect treatment is conducted. The common quality problem is the defect with the pile supporting layer in the karst area. With the coring method， not only the severity and the relative location of the defect can be detected in the pile， but also presence of the karst cave， broken zone， and the weak inter-layers. High pressure jet grouting was used to strengthen the piles with defects and cement the supporting broken zone. Inspection showed that the piles can meet the original load requirement. It can provide reference for similar projects.

Abstract:With the stress-controlled automatic GDS static triaxial gauge， the behavior of unsaturated reticulated red clay under proportional loading was studied through triaxial consolidation and drainage test at constant stress ratio for the remolded reticulate red clay with the same moisture content and dry density at different matric suctions. The experimental results show that： （1）The back pressure displacement of unsaturated reticulate red clay has an obvious turning point in the process of matric suction equilibrium at different constant stress ratios， which can be used as a marker to judge whether matric suction reaches equilibrium or not； （2）By comparing the relation curves of axial strain and time at different matric suctions， it was found that the increase of stromal suction caused the increase of axial strain； （3）Under the condition that the deviator stress remains unchanged， the increase of matric suction does not cause a significant increase of axial strain； （4）There is a linear relationship between the deviator stress and the net mean stress at different matric suctions， and its slope is approximate to the constant stress ratio； （5）A method is proposed to predict the radial strain of unsaturated reticulate red clay under proportional loading.